The invention is directed to a power source especially designed for electric arc welding using submerged arc technology. This type of welding operation requires extremely high welding currents, often in excess of 1000 amperes. Consequently, a power source for this use has generally involved robust transformer based input power supplies. In recent years, the welding industry has gradually transitioned to high switching speed inverters that have better welding performance, more accurate waveform control and smaller weight than bulky, high power transformer based power supplies. High switching speed inverters involve a series of paired switches for directing current in opposite directions through the primary of an output transformer. The secondary of the transformer is connected to an output rectifier so the output signal of the inverter based power source is generally a DC voltage. Consequently, a DC voltage to the high switching speed inverter is converted to a DC output by use of an output transformer and an output rectifier. This has been standard technology for the welding industry since the early 1990's and has been the subject of many patents for inverter power sources designed for use in welding. Blankenship U.S. Pat. No. 5,349,157; Blankenship U.S. Pat. No. 5,351,175; Lai U.S. Pat. No. 5,406,051; Thommes U.S. Pat. No. 5,601,741; Kooken U.S. Pat. No. 5,991,169; Stava U.S. Pat. No. 6,051,810; Church U.S. Pat. No. 6,055,161; and Morguichi U.S. Pat. No. 6,278,080 are all examples of inverters using an output transformer and rectifier as now used extensively in the electric arc welding field. These patents are incorporated by reference herein as background technology showing the type of high switching speed inverter based power sources to which the invention is directed. The origin of this type of high efficiency power source is low power circuits developed many years ago for lighting and other fixed loads, where the output current is quite low, such as less than 10 amperes. Through the years the welding industry has converted existing low current, high speed inverter based power sources into welding power sources with output currents in the general range of 200-300 amperes. The conversion of low capacity power sources into power sources capable of creating output currents necessary for welding involved development work generated at great expense over several years. This development work has resulted in inverter based power sources designed for electric arc welding that have high output current capabilities within maximum currents of 500-600 amperes. Indeed, The Lincoln Electric Company of Cleveland, Ohio has marketed an inverter based power source for electric arc welding having an output current capacity in the general range of 500-600 amperes. This has been the maximum current capability of the high efficiency power sources based upon high speed switching inverters with output AC transformers. Higher currents could not be obtained economically. Consequently, these inverters were not capable of use by themselves in high current welding operations, such as submerged arc for heavy pipe welding in a pipe mill. Such submerged arc welding in a pipe mill often involved the use of several tandem electrodes with each electrode requiring at least about 1,000 amperes of current, whether AC current or DC current. Consequently, inverter based power sources could not be used for submerged arc welding in a pipe mill, since each one of the tandem electrodes required at least about 1,000 amperes of welding current. The Lincoln Electric Company solved this problem by using several inverters for each electrode in the submerged arc welding operation. This technology is generally disclosed in Stava U.S. Pat. No. 6,291,798 incorporated by reference herein. This combining of several inverters allowed the pipe industry to use the high efficiency inverter based power sources in submerged arc welding of pipe sections; however, it required one or more separate power source for each electrode. This was an expensive proposition, but did have substantial advantages over other types of power sources based upon sinusoidal input transformer power supplies. Stava U.S. Pat. No. 6,291,798 is incorporated by reference to show one scheme to accomplish high current with a low current inverter based power sources. Several low current inverters connected together to accomplish high output currents are disclosed in Stava U.S. Pat. No. 6,365,874 directed to a circuit referred to as an inverter, but it is not the type of circuit to which the invention is directed. In Stava U.S. Pat. No. 6,365,874 a high capacity input transformer and rectifier produces a DC voltage which is alternately switched across the welding operation to produce an AC welding current. This patent is different from the type of inverter developed for electric arc welding, but does show the concept of using several inverters to obtain high output current. This type circuit replaces the transformer based power source for submerged arc welding. This patent is incorporated by reference herein as background information. The type of circuit shown in Stava U.S. Pat. No. 6,365,874 can be converted into a use of an inverter of the type to which the present invention is directed where the AC output current is developed by an inverter. This output concept is shown in Stava U.S. Pat. No. 6,111,216 where no specific inverter is disclosed. This patent is incorporated by reference. It discloses the concept of using an undefined inverter for AC electric arc welding wherein, irrespective of the inverter current, the high current at the polarity reversal points is reduced to decrease the required size of an output polarity switch shown in Stava U.S. Pat. No. 6,111,216 and also in Stava U.S. Pat. No. 6,365,874. These two patents are incorporated by reference as background information since when using AC output current the present invention anticipates implementation of the invention disclosed and claimed in Stava U.S. Pat. No. 6,111,216 to control the switching of the output current. However, this patent is conceptional as to the output switching concept, but not to any type of inverter detail.
The present invention is directed to a high switching speed inverter having an output transformer with a secondary rectified to produce the desired output DC voltage available for electric arc welding. In the last ten years the power sources of this type have been modified and developed to be used for electric arc welding. The present invention involves a further development in this type of power source to take the next step of essentially doubling the output current capabilities of a single inverter based power source. The invention involves several changes in the power source, one of which is the use of a matrix transformer at the output of the power source, which transformer utilizes a novel module concept allowing high current transfer from the primary to the secondary of the output transformer in the power source. The actual electrical circuit for the transformer can vary; however, a representative transformer circuit is shown in Blankenship U.S. Pat. No. 5,351,175 incorporated by reference herein as background information. The transformer modules are assemblies which form the secondary of a transformer, wherein the primary is interleaved through the modules. More than one module is used in a matrix transformer. This technology is well known and is shown in Herbert U.S. Pat. No. 4,942,353 which is incorporated herein so that disclosure of the matrix transformer technology need not be repeated. In Herbert U.S. Pat. No. 5,999,078 two adjacent magnetic cores are provided with secondary windings and primary windings wherein each module includes a half turn of the secondary winding. These modules merely provide a flat conductive strip through a core to be connected as a part of a secondary winding. The primary winding is then interleaved through the modules in accordance with standard matrix transformer technology. A similar module having several turns in a given core is shown in Herbert U.S. Pat. No. 6,734,778. These patents are incorporated herein to show prior art technology regarding modules used for a secondary winding in a matrix type transformer.